A solid-state laser is a laser that has a solid state gain medium. Semiconductor-based lasers (known as laser diodes, diode lasers, or injection lasers) are also all solid state devices, but are generally considered a separate class of lasers from solid-state lasers. Laser diodes comprise a semiconductor junction device which produces coherent radiation in the visible or infrared (IR) spectrum when forward biased so that current passes through it.
Generally, the active medium of a solid-state laser comprises a transparent crystalline or amorphous (glass) “host” material to which is added one or more “dopants”, typically a rare earth (RE) element such as neodymium, chromium, erbium, or ytterbium. Most of the common dopants are RE elements, and their operational thresholds can be reached at relatively low intensities of laser pumping. Commonly used solid-state media in which laser action is achieved include neodymium-doped yttrium aluminum garnet (Nd:YAG), neodymium-doped glass (Nd:glass), and ytterbium-doped glasses or ceramics.
Optical lasers and amplifiers having solid state gain media are conventionally optically pumped, using either a flashlamp or by laser diodes. Laser diode-pumped solid-state lasers tend to be significantly more efficient, and have become common as the cost of high power laser diode has decreased. In optical lasers and amplifiers, the RE elements in the laser rod (or core) of the laser or amplifier absorbs pump radiation of a predetermined wavelength provided by the laser diodes and, responsive thereto, provides or amplifies light of a different wavelength for propagation within the rod. For example, a typical ytterbium erbium doped glass (YbEr:glass) eye-safe laser resonator receives pump radiation having a wavelength of 940 nanometers (nm) and amplifies an optical signal having a wavelength in the 1535 nm region which propagates in the laser rod.
FIGS. 1A and 1B show two views (an end view along the solid doped laser rod (laser rod) 135 and a side view of the same, respectively) of a simplified example of a current state of the art side-pumped laser system 100 including a diode mount 120 having a plurality (e.g., 2) of pump diode bars 125 and a laser rod mount (rod mount) 130 holding the laser rod 135 embedded therein. A bond line 131 is shown between the upper and lower portions of the rod mount 130. The laser rod 135 can be 1.5 mm×1.5 mm with a corner polished flat along its length (polished pump input facet) to form a narrow window through which it is side pumped by the pump diode bars 125. A known advantage of side-pumping is that it allows the use of pump light sources with very low spatial coherence, such as high-power pump diode bars.
Device mounts as known in the art are used to secure generally cylindrical-shaped optical devices such as laser diode modules, fiber collimators and laser rod assemblies to a substrate such as an optical post, breadboard or table. The diode mount 120 and rod mount 130 are spaced apart from one another and are both separately adhesively mounted to a mounting substrate 105.
FIG. 1B shows the side view of the rod mount 130 holding a laser rod 135 embedded therein, where the laser rod 135 is reflectively coated with a reflecting outer surface at the lasing wavelength (reflecting outer surface 137, e.g., gold) except for the polished pump input facet 135′, and a composite output coupler coating (output coupler coating) 140a is on a passive Q-switch (Q-switch) 140 comprising flat optic Q-switch having doping so that the initial transmission of the path length therethrough is controlled by the doping level (e.g., cobalt doping in a spinel material), that is spaced apart from the rod mount 130 which is adhesively mounted on the mounting substrate 105. A highly reflecting (HR) mirror 116 providing essentially 100% reflectance at the lasing wavelength is on one end of the laser rod 135, and an anti-reflective (AR) coating 138 is on the other end. The HR mirror 116 and output coupler coating 140a shown on the Q-switch 140 define the optical resonator for laser system 100.
In operation of laser system 100 pump light from the pump diode bars 125 is injected through the polished pump input facet 135′ of the laser rod 135 in an otherwise coated reflecting outer surface 137. The arrows shown in FIG. 1B depict how conventional manual optical alignment is implemented by adjusting the position of the output coupler coating 140a on passive Q-switch 140 both rotationally and for tilt while its adhesive to the mounting substrate 105 is uncured or not fully cured in order to effect proper resonator alignment, such as to within 10 arc secs.